In the production of a protein or peptide by recombinant DNA technology, it is more or less common practice to have the protein or peptide expressed in the form of a fusion protein in view of the liability of the protein or peptide to be decomposed within living cells. For excision of the objective protein or peptide from the fusion protein, a chemical method for cleavage using cyanogen bromide (Itakura et al., Science, 198, 1056, 1977) and an enzymatic method using factor Xa (Nagai et al., Methods in Enzymology, 153, 46, 1987) are known.
Furthermore, as a method for cleavage of a peptide bond in a protein, cleavage of the acylcysteine bond with 2-nitro-5-thiocyanobenzoic acid is known [Seikagaku Jikken Koza 1, Tanpakushitsu-no-Kagaku II (Biochemical Experiment Series 1, Protein Chemistry II), Japanese Society of Biochemistry (ed.), Tokyo Kagaku Dojin, 247-250, 1976]. However, there is no disclosure on the excision of an objective protein or peptide from a protein.
The prior art method which involves use of cyanogen bromide cannot be applied to the production of methionine-containing peptides, while the method involving use of factor Xa has drawbacks, for example in terms of excision yield.
Therefore, a demand exists for a technology by which an objective protein or peptide may be efficiently excised from a fusion protein or peptide.
The inventors of the present invention explored in earnest for a technology by which the novel bioactive peptide 19P2 ligand (19P2L, which is named as a "prolactin-releasing peptide (PrRP)" in Hinuma et al., Nature 393, 272-276, (1998)) may be produced with high efficiency and found that 19P2L can be efficiently produced by preparing a fusion protein or peptide comprising 19P2L fused to a protein or peptide having cysteine at its N-terminus and subjecting the fusion protein or peptide to a peptide bond cleavage reaction. The inventors did further research on the basis of the above finding and have accomplished the present invention.